1. Field of the Invention
This invention relats to a method of producing a bent resin tube.
2. Description of the Prior Art
Conventionally, a bent resin tube has been produced by taking the following procedures. First, as shown in FIG. 13(A), a straight resin tube 100 is prepared, and inserted in a whole contraining die 102 having a U-shape cross section and a length corresponding to the length of the tube 100 so as to constrain the shape of the whole tube 100. Second, the die 102 having the tube 100 therein is placed in a heating oven, and heater, for example, at 150.degree. to 160.degree. C. for 20 to 30 minutes, thereby rendering a bend shape to the tube 100. Then, the die 102 is taken out of the oven and cooled, and the bent resin tube is released from the whose constraining die 102.
Otherwise, as shown in FIG. 13(B), the straight resin tube 100 is constrained in a bend shape by a plurality of pulley dies 104, and the tube 100 and the pulley dies 104 in that state are heated in a heating oven to render the bend shape to the tube 100. Then procedures similar to the above are taken.
In these conventional methods, however, the dies 102, 104 for constraining the shape of the whole resin tube 100 have a considerable heat capacity in themselves, and it is necessary to heat the die 102 or 104 to a predetermined temperature in the oven. Accordingly, it takes a long time to heat them in the oven, and to cool them after taken out of the oven. For these reasons, the production of bent resin tubes has a poor efficiency. Moreover, for example, in the case of producing resin tubes as long as 3 to 4 meters, a large size oven is required, and the cost of equipment is considerably high.
In addition, in these conventional methods, when the curvature of the bent portion, i.e., the bend radius of the bent portion is small, forcible bending of the resin tube 100 has a possibility of causing a kink. To avoid this phenomenon, the straight tube 100 must be preheated before inserted in the bending die 102 or 104. This preheating also prevents the improvement of the production efficiency.
Further, in these methods, hand labor is required to insert the resin tube 100 into the bending die 102 or 104. Moreover, different whole constraining dies are necessary for different desired bend shapes of resin tubes.